This application claims priority to Japanese Patent Application Nos. JPAP2000-003000 filed on Jan. 11, 2000, JPAP2000-035757 filed on Feb. 14, 2000, and JPAP2000-391209 filed on Dec. 22, 2000, in the Japanese Patent Office, the entire contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus that can conveniently be upgraded to a duplex image fonning apparatus.
2. Discussion of the Background
An electrophotographic image forming apparatus is widely used in various machines, such as copying machines, laser printers, facsimile machines, etc. In such electrophotographic image forming apparatus, an electrostatic latent image is formed on a photoconductive member and is developed, with toner, into a toner image, which is then transferred and fixed onto a recording sheet made of plain paper. As penetration of the electrophotographic image forming apparatus increases, requirements for a compact size and a light weight are increased.
In order to remain within the scope of the above requirements, various efforts have been made, such as, for example, a length of a sheet transfer path, for transferring a recording sheet inside the apparatus, has been shortened. In addition, an interior layout of the apparatus has been designed for a better machine handling in case of problems, such as a paper jam. For example, a sheet cassette is located at a lower part, fixing and ejection units are located on an upper part, and the above lower and upper parts are connected to each other with a vertical sheet-path. Furthermore, an operation panel is mounted on a front surface of the machine, typically in small-sized and mid-sized machines.
In addition, a requirement for a duplex printing function has recently been increased in connection with a movement of natural resource preservation. To cope with such a requirement, an image forming apparatus, employing the above-mentioned machine design, and which is capable of adopting an add-on duplex unit, has been developed. A published Japanese Unexamined Patent Application, No. 6-110274, described an example of such duplex image forming apparatus, as shown in FIG. 1.
In the duplex image forming apparatus of FIG. 1, a sheet flipping unit 130, for flipping a recording sheet during a duplex image forming process, is mounted on a top and front part of the apparatus. In the front side, the apparatus is provided with a manual sheet insertion guide 140.
In the duplex image forming apparatus of FIG. 1, a recording sheet is transferred from a sheet cassette 141 during a duplex print mode, in which an image print is performed on both surfaces of the recording sheet. The recording sheet is stopped by registration rollers 142 and is restarted in synchronism with the rotation of a photoconductive drum 151. After that, the recording sheet proceeds to a process unit 150 having the photoconductive drum 151. When a recording sheet is inserted from the inlet of the manual sheet insertion guide 140, the recording sheet also proceeds to the process unit 150, via a manual sheet insertion path 143.
In the process unit 150, the recording sheet is subjected to an image forming process on its front surface and, as a result, the recording sheet has a toner image on the front surface. After that, the toner image is fixed with a heat fixing unit and is transferred upwardly. When a sensor 152 detects the leading edge of the recording sheet, a switch pawl 131 is turned to a position indicated by solid lines in FIG. 1.
When the switch pawl 131 is at this position, the recording sheet is forwarded into the sheet flipping unit 130. More specifically, the recording sheet is transported by a pair of switchback rollers 132 so that the leading edge of the recording sheet is ejected over a stacker 133. When a sensor 134 detects the trailing edge of the recording sheet, the switchback rollers 132 are reverse rotated so that the recording sheet is reverse transferred towards an exit 136 through a sheet path 135 in the sheet flipping unit 130. After that, the recording sheet again proceeds to the process unit 150 via the manual insertion path 143. In the process unit 150, the recording sheet is subjected to the image forming process, but on its back surface this time. As a result, the recording sheet is printed on both front and back surfaces.
After that, the recording sheet is guided to a pair of ejection rollers 137 by the switch pawl 131, which is by now turned to a position indicated by dotted lines. The recording sheet is then ejected with the ejection rollers 137 onto stacker 133.
As another example, a published Japanese Unexamined Patent Application, No. 7-261471, describes an image forming apparatus capable of having an add-on duplex unit. In this example, an opening to an outside is formed in a pair of sheet transfer paths downstream from a fixing unit in a sheet transfer direction. A duplex unit is attached to the image forming apparatus such that a sheet inlet is fit with the above opening. When the recording sheet is flipped, the leading edge of the recording sheet is ejected to an outside from the duplex unit or over an eject tray from the image forming apparatus.
In the above image forming apparatus, the operator is needed to open a front cover to deal with a paper jam or to exchange consumable items, since the apparatus has the design of the front operation panel and the vertical sheet transfer path, as described below. Therefore, if the duplex unit is attached to the front of the apparatus, the duplex unit becomes a severe obstacle and the inside accessibility of the apparatus is decreased.
In addition, a front design of the image forming apparatus would have a relatively large difference between those having the duplex unit and those having none. Accordingly, various components associated with the front design could not be unified and therefore, a consistency of machine model may become difficult.
Furthermore, in the image forming apparatus described in the published Japanese Unexamined Patent Application Nos. 6-110274 and 7-261471, a part of the recording sheet is temporarily ejected outside the apparatus and is reverse transferred during the sheet flipping process for the duplex image forming operation. Accordingly, there is a risk that the recording sheet is accidentally touched or held by anything, such as the operator, when the recording sheet is temporarily ejected outside the apparatus during the duplex image forming operation. As a result, the recording sheet may be jammed inside the apparatus. When the ejected part of the recording sheet touches other recording sheets stacked on the stacker, it is possible that other recording sheets may be pushed away.
The present invention provides a novel image forming apparatus. In one example, a novel image forming apparatus includes a sheet cassette, a first sheet path, a first sheet transfer mechanism, an image recording mechanism, an ejection mechanism, a second sheet path, and a sheet flipping mechanism. The sheet cassette is configured to contain a plurality of recording sheets. The sheet cassette is located at a lower part of the image forming apparatus. The first sheet path is arranged on a side of the apparatus. The first sheet transfer mechanism is configured to send a recording sheet one by one from the sheet cassette through the first sheet path. The image recording mechanism is configured to perform an image recording process relative to the recording sheet sent by the first sheet transfer mechanism. The ejection mechanism is configured to switch between an ejection process and a duplex recording process relative to a back surface of the recording sheet after completion of the recording process on a front surface of the recording sheet. The second sheet path is configured to receive the recording sheet from the ejection mechanism, when the ejection mechanism switches to the duplex recording process, and to transfer the recording sheet back to the image recording mechanism. The second sheet path is arranged on other sides of the apparatus than the side of the apparatus for the first sheet path. The sheet flipping mechanism is configured to flip the recording sheet in the second sheet path and to have a flipping space in which the recording sheet is flipped without coming outside the apparatus. The sheet flipping mechanism is arranged along the second sheet path.
The first sheet path may be arranged in a front part of the apparatus.
The second sheet path may be arranged in a rear and top part of the apparatus, a rear part of the apparatus, and under the sheet cassette.
The sheet flipping mechanism may be arranged in a rear part of the apparatus.
The sheet flipping mechanism may include a guide plate configured to deflect a leading edge of the recording sheet hung down in the flipping space of the sheet flipping mechanism.
The sheet flipping mechanism may be arranged under the sheet cassettes.
The sheet flipping mechanism may include a sheet flipping roller, a driving roller, and a trailing edge detect sensor. With the above configuration, the sheet flipping roller is configured to be rotated forwardly and backwardly so as to transfer the recording sheet temporarily to the flipping space and then back to the second sheet path. The driving roller is configured to be rotated forwardly and backwardly in synchronism with the sheet flipping roller so as to transfer synchronism with the sheet flipping roller so as to transfer the recording sheet temporarily to the flipping space and then back to the second sheet path. The trailing edge detect sensor is configured to detect a trailing edge of the recording sheet when the recording sheet is transferred out of the second sheet path and into the flipping space. The trailing edge detect sensor is arranged in a position between the sheet flipping roller and the driving roller. When the trailing edge detect sensor detects a trailing edge of the recording sheet, the sheet flipping roller and the driving roller are rotated in a reverse direction to reverse transfer the recording sheet back to the second sheet path.
The sheet flipping mechanism may further include a switch pawl configured to conduct the recording sheet into the flipping space, until the trailing edge detect sensor detects the trailing edge of the recording sheet, and to conduct the recording sheet back to the second sheet path, after the trailing edge detect sensor detects the trailing edge of the recording sheet.
The above-mentioned image forming apparatus further includes a second sheet transfer mechanism configured to transfer the recording sheet. Further, the second sheet path is divided into three portions and is included in each of the ejection mechanism, the sheet flipping mechanism, and the second sheet transfer mechanism.
Each of the ejection mechanism, the sheet flipping mechanism, and the second sheet transfer mechanism may be configured to be a separate add-on unit.
A vertical sheet path portion of the second sheet path may include a door portion and an interior of the apparatus is made accessible when the door portion is opened.
The door portion may have a cover, including one of a pair of guide plates, and an inside plate, including the remaining one of the pair of guide plates. In this configuration, the cover is configured to be opened so that the inside plate is made accessible when the cover is opened.
The inside plate may be configured to be opened so that an interior of the apparatus is made accessible when the cover and the inside plate are opened.
The cover and the inside plate may be mounted on the apparatus with a common shaft.